Although phosgene, COCl.sub.2, is a widely used article of commerce, carbonyl cyanide, CO(CN).sub.2, the cyano analogue of phosgene, is used only sparingly. In large part this difference in utilization arises from difficulty in preparing carbonyl cyanide. Carbonyl cyanide is used in the preparation of cyanoformates, affords Diels-Alder adducts with some dienes, and recently has been used in the preparation of ene adducts (Kociolek and Leplawy, Synthesis, 778 (1977)) and in preparing a class of cyanopolyesters (E. G. Banucci, Synethesis, 671 (1973); J. Polymer Sci., 11, 2947 (1973)).
Among the prior art methods of preparation, oxidation of tetracyanoethylene is, perhaps, the most developed route to carbonyl cyanide (E. L. Martin, Org. Syn., 51, 70 (1971)). Alternate methods of preparation include the reaction of carbonyl fluoride with potassium cyanide dissolved in a melt of lithium chloride and potassium chloride at 400.degree. C. (W. Verbeek and W. Sundermeyer, Angew. Chem., internat. Edit., 6, 871 (1967)) and pyrolysis of acetoxyiminoacetic cyanide (O. Achmatowicz and M. Leplawy, C. A., 10033d (1959)).
Phase transfer catalysis is a technique of much interest in recent years. See C. M. Starks, J. Amer. Chem. Soc., 93, 195 (1971); J. Dockx, Synthesis, 441 (1973); G. W. Gokel and W. P. Weber, J. Chem. Educ., 55 350, 429 (1978). In this process a reagent, called a phase transfer catalyst, when added to an aqueous phase in contact with an immiscible organic phase forms an ion-pair with the ionic component present, e.g., a cyanide salt. Because the formed ion-pair has appreciable solubility in organic solvents it is carried, at least in part, across the phase boundary from the aqueous to the organic phase, where it retains its identity as ion-pair. This ion-pair in the organic phase then can react with another component dissolved in the organic phase to form the desired product. Because this reaction occurs homogeneously its rate is greater than when the reaction is conducted heterogeneously, and undesirable side reactions otherwise present may be diminished or even eliminated. After reaction, a different ion-pair is formed involving the phase transfer catalyst and this new ion-pair crosses from the organic into the aqueous phase where the phase transfer catalyst is again available to form an ion pair with an ionic reactant in the aqueous phase, e.g. cyanide ion. Thus, the phase transfer catalyst truly acts as a catalyst and needs to be employed in less than stoichiometric amounts.
In a variant where the phase transfer catalyst is soluble in the organic solvent, the ionic reactant is used as a solid rather than in aqueous solution. This variant may be referred to as solid-liquid phase transfer catalysis, whereas that described in the prior paragraph may be referred to as liquid-liquid phase transfer catalysis.
Phase transfer catalysis has been used in the preparation of acid cyanides, RCOCN, from acid halides (K. E. Koenig and W. P. Weber, Tetrahedron Letters, 2275 (1974)). The technique of phase transfer catalysis is particularly useful in the preparation of cyanoformates, ##STR1## (M. E. Childs and W. P. Weber, J. Org. Chem., 41, 3486 (1976)). Significantly, these latter authors report that the attempted preparation of carbonyl cyanide by reaction of phosgene-the dichloride of carbonic acid-with potassium cyanide under conditions of phase transfer catalysis failed under a wide variety of experimental conditions.